1. Field
Embodiment of the present disclosure relates to an electrically controlled brake system, and more particularly, to an electrically controlled brake system that maintains hydraulic pressure supplied to each wheel cylinder using a cut valve.
2. Description of the Related Art
Recently, active hydraulic booster (AHB) systems are installed in vehicles such as hybrid vehicles, fuel cell vehicles, and electric vehicles.
Generally, an electrically controlled bake system, for instance, an AHB system, is a brake system in which, when a driver steps on a brake pedal, an electronic control unit (ECU) which performs overall control of the system detects the stepping, generates a hydraulic pressure using a hydraulic power unit (HPU), supplies the hydraulic pressure to a master cylinder, transfers a brake hydraulic pressure to each wheel cylinder of wheels using an electronic stability control (ESC) system which controls a brake force of each wheel, and generates a brake force.
Such an AHB system generates a pressure needed to brake by controlling valves when a driver brakes. The valves used in valve control include an apply valve for supplying the hydraulic pressure to the wheel cylinders, a cut valve for maintaining the supplied hydraulic pressure, a release valve for discharging the hydraulic pressure supplied to the wheel cylinders, and a simulation valve for generating a pedal effort of the brake pedal.
When the AHB system operates normally and the driver steps on the pedal, the AHB system is operated by receiving a brake pedal signal, the apply valve is opened according to the operation of the AHB system, a high pressure brake fluid which filled an accumulator passes through the apply valve and is supplied to a booster circuit (BC), and a pressure of the BC is increased. Simultaneously, the cut valve is blocked and the brake pressure is maintained. In addition, while the simulation valve is opened, a pressure of a pedal simulator which corresponds to a reaction force of the brake pedal is generated by a spring in the pedal simulator being pushed by the hydraulic pressure in the master cylinder.
When a mechanical leak occurs in the cut valve which maintains the supplied hydraulic pressure, while the driver steps on the brake pedal and an input rod connected to the brake pedal is moved forward, an output rod of the master cylinder may strike the input rod due to the leaked hydraulic pressure. Therefore, a kick back in which a physical impact is transferred to the brake pedal connected to the input rod occurs due to the output rod striking the input rod. The driver may feel vibrations of striking the brake pedal due to the kick back phenomena, and thus, the driver may feel discomfort.
However, since a logic which determines whether a mechanical leak failure of the cut valve occurs is not implemented in a conventional case, the driver may feel discomfort or be threatened by an occurrence of the kick back phenomena when the failure actually occurs.